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Typically you would run a single line from the PVB that supplies all of the zone valves. That line can run from one side of the house to the other. Then simply tee the valves in where you would like and run your heads from there. If you really wanted to run back through the house after the PVB, you could, but I don't think there would be any advantage. You would actually have a second piece of copper exposed that would not need to be.

While you will find everyone has different opinions, there are MANY who consider a double check valve to NOT be adequate back-flow protection if you plan on using fertigation. You can learn more by reading through irrigationtutorials.com, but comes down to this...

Irrigation water is not severely contaminated water. Some yucky thing can and do get sucked back in to the pipes. But even if you didn't have ANY backflow preventor and irrigation water found it's way back into the house, the contamination level is relatively low. This would NEVER be a desirable thing, but using ANY sort of a backflow preventer coupled with this fact makes the typical irrigation installation relatively safe (i.e. backflow preventers rarely fail, and if it does, it's not a catastrophy).

But with firtigation, you are talking about injecting "stuff" into the water making it highly contaminated therefore the confidence level of the backflow must be high. Generally, a double check is NOT considered safe enough for this type of situation because a double check can easily fail (relative to other back-flow-preventors) if debris in the water lodges in the valve preventing it from properly closing. (If you don't thing there are "things" in your water, even if it's city water, empty the hot water heater and see what has settled out of the water). While I'm not sure about PVB, its the RPZ that many consider to be required when dealing with contaminated water (such as injecting fertilizer into it). The RPZ is designed such that even if it's valves fail because of debris, any attempt of the water to flow back is prevented by the relieve valve.

You can install an RPZ in the house (and like double checks, the elevation doesn't matter like it does with PVB), but you must allow drainage from the relieve valve.

BTW, RPZ doesn't have to be that expensive. The local Lowe's was selling 3/4" Watts RPZ (009 I believe) for as little as $116.

True! You can install a double check valve or reduced pressure valve all inside so you dont have to even come out and back in. Here in RHode Island code dows not allow dual checks and RP valves are to expensive for residential. All contractors pretty much install the PVB.

Hmmm....I don't think that's entirely accurate. To my understanding, there are some backflow units that can be mounted without concerns for altitude. I'm pretty sure the double check units would be an example. I will probably be installing the backflow above ground so I'm not going to worry about that part so much right now. Probably my bigger curiosity would be if it's OK to split the output AFTER the backflow in my basement. Again, this is assuming I went back into the basement on the output of the backflow unit. I'd like to be able to have valves mounted on both sides of the house so I don't have to run so many poly pipe runs around my house (and my huge deck). Or maybe I can have valves on both sides of the house WITHOUT running it through the basement....but instead by running just one poly pipe around the house/deck to another set of valves.

Either way you can never hide your backflow. It needs to be installed atleast 12" higher than your highest sprinkler head. You would see pipe either way on the outside of the house. You might want to consider connecting your fertigation connection to the main outside also and just run the feeding tubes in the house to the tank

Fertigation in basement?

I'm looking at a design that will use fertigation. I'd like to put the fertigation unit in my basement (we live in Western NY). I haven't completed my research on backflow protection. I do understand that some types of backflow can be located in the basement. That would be great, but my hunch is that the backflow will need to be outside. I have 3/4" supply, 5/8" water meter, and 70psi. I'm thinking about attaching 1" copper right after the meter (through a shutoff valve) going straight up to the top of my basement, go outside, go throught a backflow unit, then come back into the basement again. Now go through the "basement located" fertigation unit. Next I would "fork" the 1" copper pipe so I could send a run to the other side of my house (ceiling of basement). Both "forked" copper lines would now go outside again to the valve manifolds (buried in ground). When I run the copper outside, do I just go out (over the foundation wall), then down into the ground (hence you'd see the pipe). Or do I drill through the concrete to keep the pipe buried? I'm guessing the former. If I don't do this "out, then in, then out again" routing of pipe through my basement, how do I combine an "outdoor" backflow unit with fertigation that should be indoors? Thanks for any help.